What is HDR photography?

Exploring high dynamic range options on your digital camera

Home on the (contrast) range

Squinting westward at the ridgeline of the Tetons from the valley floor below, you survey the shot. There’s a rock-strewn shallow stream in the foreground. The sun is beginning to set behind the jagged range. But even with your eye, it’s tough to get a sense of the true grandeur of the panorama in front of you, because the contrast is too extreme. You put on your sunglasses, and now you’ve stopped squinting – but the shadows are just blobs of black.

Sound familiar? While you may never have seen the Tetons, it’s a solid bet your eyes have encountered similar challenges almost every day. And if your eyes struggle in this situation, just think of what it’s like for a digital camera.

A solution appears

Early pioneers in photography addressed this problem by taking two different shots of a problematic subject. One was exposed for highlights, like the sky and clouds, and the other was taken to reveal detail in shadow areas, like backlit trees. In the darkroom, they’d combine the highlights from one negative with the shadows from another, while masking off the badly exposed portions of each. This technique was the dawn of high dynamic-range imagery, or HDR for short.

Taming contrast extremes

In essence, the same concept is applied to what we call HDR today, although techniques and tools have evolved to suit the strengths of digital photography. At its most basic level, HDR photography today involves taking a variety of exposures of a subject in quick succession (at least three or more). Then, the images are blended, using either the camera’s built-in processor or specialized software loaded on your computer. The goal is to enhance detail over portions of the image that would be problematic with conventional single-shot exposures.

So take a look at the series of shots below of our snow scene at Wintergreen Resort in Virginia's Blue Ridge, shown left to right from darkest exposure to brightest. Note how the shadow areas are well-defined in the brightest exposures, and the darkest exposures reveal detail in the highlights:

Three exposures were blended to achieve our final high dynamic-range image, below. Click for larger image.

Now, take a look at our HDR blend, tweaked in software to show the detail in both extremes, while leaving well-exposed portions of the shot largely unaffected:

Is it real? Or too real?

Modern image processing software allows for a multitude of ways to process and merge similar images. What we’ve done above is really a subtle adjustment of overall image contrast. Sometimes, what a photographer may casually refer to as HDR may more accurately be called “tone mapping.” This is where different regions of the picture are subjected to different blending techniques, often to hyper-realistic or surrealistic effect. Such images are arresting, but seldom very naturalistic. That's not a bad thing, just a creative choice.

For your consideration

Though today’s digital cameras have made great leaps in capturing high-contrast subjects in a single shot, it’s always worth considering the HDR technique whenever you’re looking at challenges like the one described in our opening paragraph. Note that it’s not the best choice for fast-moving subjects, due to the time-lag between multiple exposures. HDR tends to be better suited to landscapes and still-life subjects. And while software designed to merge separate exposures can do a good job of aligning the subtle variances of handheld HDR exposures, using a tripod can up your chances for good results.

While you can manually take shots at different exposures in quick succession and merge them in an image-processing software suite like Adobe Photoshop®, many digital cameras these days have a specialized HDR mode that takes care of the sequential exposure settings for you. Some even take their best guess at a desired blend and present it as a finished image for your approval. Bear in mind, the more drastic the spread between the darkest and brightest parts of your image, the bigger the range should be in your various exposures that make up your HDR composition. The goal is to see defining detail in every part of the picture, and not to have large areas of 100% white or 100% black. So your component exposures should be set accordingly.

Like many photographic techniques, trial and error will make you better. A vital part of this technique is learning about software-assisted photo editing. The aforementioned Adobe Photoshop, Adobe Lightroom®, Apple® Aperture®, or HDRsoft's Photomatix Pro are great places to start learning to play with tone mapping. Within minutes of sitting down to play, you'll be looking at the world in a very different way.

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